The summit with Turkey's Erdogan and Iran's Rouhani comes two days after Putin hosted surprise talks with Syria's Assad
Russian President Vladimir Putin said on Wednesday a “new stage” had been reached in the Syria crisis but achieving a political solution would require compromises from all sides, including the Syrian government.
Syrian opposition groups, meeting in Saudi Arabia to seek a unified position ahead of peace talks, decided to stick to their demand that Assad leave power, Al Arabiya television reported, following speculation they might soften their stance after their hardline leader quit.
Putin was speaking alongside Turkish President Tayyip Erdogan and Iranian President Hassan Rouhani in the southern Russian city of Sochi.
The summit at the Black Sea resort came two days after the Russian leader hosted surprise talks with the war-torn country's president, Bashar al-Assad.
"It is obvious that the reform process will not be simple, it will require compromise and concessions from all parties, including obviously the Syrian government," Putin said.
"I count on the fact that Russia, Iran and Turkey will put in their best efforts to make this work as productive as possible," he added.
Putin added that there was a "real chance" to end Syria's war which monitors say has killed more than 330,000 people as he said Russia, Turkey and Iran had managed to prevent the collapse of the war-torn country.
Turkey's Erdogan for his part said the three countries had to intensify efforts to try to settle the crisis.
"We need to make significant progress on the political solution," he said in translated remarks.
"I believe that we will make critical decisions here."
Iran's Rouhani said the three countries' strategy was "based on partnership and not competition, on friendship and not on animosity".
"By cooperating, our countries destroyed the decaying body of terror" in Syria, he said.
'It is obvious that the reform process will not be simple, it will require compromise and concessions from all parties, including obviously the Syrian government'
- Russian President Vladimir Putin
Russia claims to have practically ended the military conflict through its intervention, but the various sides in Syria are far from a political agreement.
Ahead of Wednesday's summit in Sochi, Putin discussed Syria with his US counterpart Donald Trump and Saudi Arabia's King Salman, among other leaders.
In a lengthy phone call late Tuesday, Putin and Trump stressed the need to ensure "the stability of a unified Syria," the White House said.
Syria is divided between forces loyal to Kremlin-allied strongman Assad, the US-backed Syrian Democratic Forces (SDF) and several militant groups and rebel units.
Multiple rounds of talks hosted by the UN have failed to bring an end to the conflict.
Other initiatives including those spearheaded by Moscow have also failed to bear much fruit.
Encouraged by military progress of the Russian and Syrian forces on the ground, Putin is hoping to breathe new life in the stuttering negotiations.
Government forces have gained the upper hand on the battlefield with Russia's help, including recent victories against the Islamic State group and a fresh drive against rebels near Damascus.
Russia's President Vladimir Putin embraces his Syrian counterpart Bashar al-Assad on 20 November (AFP)
Putin said in comments released on Tuesday that "thanks to the Russian army, Syria has been saved as a state."
Moscow, Ankara and Tehran are cooperating with increasing intensity on ending the civil war, even though Turkey backs the rebels, at odds with Russia and Iran.
The Syrian president's fate remains a stumbling block, preventing global players from reaching a peace settlement.
During their phone call on Tuesday, Putin told Trump that "the Syrian leader confirmed his commitment to the political process, (and) conducting constitutional reform and presidential and parliamentary elections."
Assad said he wanted to advance negotiations.
"We don't want to look back and we are ready for dialogue with all those who want to come up with a political settlement," Assad said in translated comments.
Wednesday's summit comes ahead of parallel UN-led talks in Geneva set for 28 November.
Russia, Iran and Turkey have backed negotiations in the Kazakh capital Astana that have brought together the representatives of the opposition and the regime.
Those talks led to the creation of four so-called "de-escalation zones" that produced a drop in violence, but fighting and bombardments continued with many casualties in recent weeks.